Rapid curing composition and method

ABSTRACT

Use of a phytic acid catalyst in accelerated curing of thermosetting coatings.

. 260/928; 117 132 B, 132 BE 0 United States Patent 1 [111 3,767,461

Eiland Oct. 23, 1973 RAPID CURING COMPOSITION AND METHOD [56] 7 References Cited [75] Inventor: Ehrlich M. Eiland, Lower Burrell, UNITED S ES PA ENTS Pa. 3,003,983 10/1961 Cox 260/292 TN [73] Assignee: Aluminum Company of America, musburgh, 2,976,170 3 1901 Eiland 117/49 [22] Filed: Aug. 31, I972 Primary Examiner-Morris Leibman [21] Appl' 285473 Assistant Examiner-P. R. Michl I AttorneyAb1-am W. Hatcher [52] US. Cl... 117/132 B, 117/132 BE, 260/328 R,

260/328 EP, 260/334 R, 260/33.4 EP, [57] ABSTRACT 260/336 260/336 UA Use of a phytic acid catalyst in accelerated curing of [51] Int. Cl B44d 1/36 thermosemng coatings [58] Field of Search 260/775 AB, 2 EP,

10 Claims, No Drawings 1 RAPID CURING COMPOSITION AND METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to curing thermosetting coat-f ings on a substrate. More particularly, it relates to accelerating the curing of thermosetting coatings on metal substrates such as aluminum, especially foil or, sheet, for example, can sheet, by use of a special catalyst. When I refer to aluminum, I include aluminum and aluminum base alloys containing at least SOpercent by weight aluminum.

2. Description of the Prior Art In U. S. Pat. No. 2,976,170 I disclosed a method for rendering aluminum foil receptive to adhesion of thermoplastic coatings by treating the surface with phytic acid.

SUMMARY OF THE INVENTION ins such as thermosetting epoxies and vinyls. Essential ingredients of these coatings for the quicker and easier curing on the substrate-are one or more resins, asolvent for the resin or resins-andwhephytic acid. They may also contain a cross-linking agent-and otheringredients, for example, pigments, dyes and the like such as conventionally added to coating resin compositions. When I refer hereinto the resin componentof'the coating, I include use of more than one cross-linking resin as said resin component, as will be illustrated in the ex-. amples hereinafter.

The resin orcombination of 'resinsis cured by heating, for example, in an oven. Generally-the. highest temperature required for curing according to theinvention is 600 F, above which point some foil strength may be lost due to annealing, when the substrate is aluminum foil. Only a few seconds are required for-curing the resin. Thicknessof the curedrcoating generallyvaries from about 1 to about mg/inhThe time required for curing is usually less thanabout 10 seconds. The phytic acid may be added to the coating composition dissolved in an alcohol such asbutyl, for example, 50:50 byweight.

DESCRIPTION OFTI-IE PREFERRED EMBODIMENTS The following examples are illustrative of the invention.

v, 7 EXAMPLE 1 An epoxy-urea formaldehyde coating of approximately the following composition was applied to a sample of 1,145 (Aluminum Association designation) aluminum foil. I

Weight Material 16.4 Epon 1007' epoxy resin (Shell Chemical 22.7 Beckamine P196-60 urea formaldehyde (Reichold Chemical Co.) (60% resin) 60.9 Methyl Ethyl Ketone 0.3 50% phytic acid in water the chemical structure of a typical molecule of Epon resin is as follows:

The melting point by the Durrans mercury method is 125135 C, the color, 25 C (Gardner) ofa 40 percent weight solution in butyl carbitol at 25 C 5 max., viscosity, 25 C (40 percent in butyl carbitol) Y-Z (Gardner-Holdt), 1828 poises and the epoxide equivalent (grams of resin containing one gram-equivalent of epoxide) 2,000-2,500.

The coating was cured on the foil in a 2-zone oven, the first zone being operated at a temperature of 350 F and the second at 400 F. The same coating, except for omission of the phytic acid, was applied to another sample of 1,145 aluminum foil. It required a curing temperature of 600 F in the first zone and 700 F in the second. The phytic acid-containing coating was cured at'the rate of 350 ft/min, whereas the sample without catalyst was cured at only 250 ft/min. The catalystcontaining coated foil remained in the oven for curing only 5 seconds, whereas the non-catalytic coated foil required 7 seconds for curing. Cured coating thickness for both coatings was 1.25 mg/in.

EXAMPLE 2 Substantially the same compositions as used in Example I were cured on 1,145 aluminum foil in a 6-foot drying tunnel. The sample without the catalyst required a curing temperature of 490 F, whereas the sample with the phytic acid was cured at only 375 F. Both samples were cured at the rate of 25 ft/min to give a cured coating of 3 mg/in.

EXAMPLE 3 The following thermosetting vinyl coating composition was cured on 1,145 aluminum foil to a thickness of l.8'mg/in by passing through aheating zone at a rate of ft/min and a temperature of 550 F and'compared with the same composition similarly cured exapproximately 91 percent by weight vinyl chloride, 3 percent by weight vinyl acetate and 5.9 percent by weight other (hydroxyl calculated as vinyl alcohol), approximate specific gravity 1.39, viscosity at 25 C of a 1/1 MlBK/toluene solvent ratio solution 200-400 CPS.

Both compositions remained in the heating zone for 7 seconds. The composition without the catalyst was rubbed through to theunderlying foil by one double rub with a rag soaked in methyl ethyl ketone, whereas it took double rubs before the underlying foil coated.

with the, phytic acid-containing composition was reached.

EXAMPLE 4 lpercent phytic acid (40percent in water) based on coating solids was added to an epoxy coating which was applied to aluminum foil and cured at 325 F for 30 seconds. Good resistance to methyl ethyl ketone (MEK) and good adhesion on forming were obtained.

EXAMPLE 5 A comparison was made between adhesion after deformation and degree of cure on foil of an epoxy resin catalyzed by a prior art catalyst which did not contain phytic acid and the same resin containing phytic acid. As rolled 1,145 foil 0.004-inch thick was used. The prior art catalyst was added at 45 cc per gallon and the phytic acid (40percent active) was used at 0.3 lb per 83 lb clear epoxy. Drying was at 400 F for 5 seconds. Results showed removal of the conventionally catalyzed lacquer after 4 to 7 rubs with methyl ethyl ketone (MEK), whereas the phytic acid-catalyzed lacquer lasted for 30 to 50 rubs before lacquer removal. Adhesion on dead folding also proved better for the phytic acid-catalyzed lacquer.

EXAMPLE 6 A white-pigmented epoxy resin was tested in a manner similar to that employed in Example 5, both with and without phytic acid catalyst. The phytic acid catalyst resulted in a faster cure and better adhesion than the prior art catalyst.

EXAMPLE 7 An attempt was made to apply 2 lbs per 3,000 sq ft of a prior art-catalyzed red epoxy which contained no phytic acid to two sides of 0.00045in. 1145 as-rolled foil. A prior art catalyzed red polyester was also tried. Because of the high temperature required for curing,

severe wrinkling of the foil occurred in both instances.

The following composition was then made up and applied:

Weight Material 132 Mobil Chemical Co. S-8988-002-c1ear epoxy 25 lnmont RBH Div. Watchung Red epoxy pigment dispersion 40 Solvent: (45MEK 45 Toluol 10 isopropanol) by volume 0.28 50% phytic acid This coating was applied using a conventional coating machine and cured satisfactorily at above 100 F lower oven temperature than for the above red epoxy and red polyester phytic acid-free coatings. Drying conditions were 25 ft/min web speed, oven tunnel temperature 350 to 450 F and tunnel roll temperature 180-210 F. At the lower curing temperature, made possible by using phytic acid, the wrinkling of the foil was eliminated.

EXAMPLE 8 An epoxy slip coat was catalyzed with an amount of phytic acid (lOOpercent active basis) equal to 0.2percent by weight of the coating. Curing requirements and web speed for the phytic acid-catalyzed coating compared with the same coating employing a prior art catalyst were as follows:

Web Speed Catalyst Ft/Min. Tunnel Zone 1 Tunnel Zone 2 Prior Art 250 600F 700F Phytic Acid 350 350F 400F EXAMPLE 9 Addition of about 0.2percent IOOpercent active) phytic acid by weight, based on total coating weight, to a thermosetting vinyl polymer resin (Mobil Chemical Co. 8-8998-001) permitted curing on aluminum foil to high solvent resistance at relatively low temperature. The lacquer cured with phytic acid prevented migration of pigment. At the same time curing temperature 600 F) was low enough to prevent undesirable discoloration of the lacquer or brittleness caused by undesirable annealing which sometimes occurs when curing is done without using a phytic acid catalyst. In this instance the coating composition was as follows:

Grams Material 79.7 Mobil Chemical Co. thermoset vinyl 19.9 MEK Toluene 1:1

0.4 Phytic acid (50% active acid) The coating was applied at 1.8 lb per 3,000 sq ft to annealed foil, dried at 400 F for 15 seconds, and cured to the point where no coating was removed by 50 double rubs with methyl ethyl ketone. Adhesion to the foil was good, and clear Mobil 8-1299 thermoplastic vinyl adhered well when applied over the coating. For comparison, when S8998-001 thermoset vinyl, which contained no phytic acid catalyst, was applied and dried in the same manner, cure was unsatisfactory, and the coating was removed with only 12 double rubs with MEK.

Similar tests were made using Mobil x68 green and 70X682 purple, which are pigmented versions of the aforementioned 8 8998 001 clear therm oset vi- U nyls. Equally good results as with the clear were found with these colored coatings.

Further tests made according to the same procedure were conducted on 0.004 in. 1,145 aluminum foil using coating with and without phytic acid catalyst. Under the same curing conditions of 400 F, this time for 20 seconds, the acid-catalyzed coating gave better adhesion on forming than the uncatalyzed coating.

EXAMPLE 1O 50 grams of phytic acid (50percent active) were added to 50 grams of butyl alcohol and boiled for 2 hours, 45 minutes. There was some brownish precipitate. This was allowed to settle, leaving liquid on top. The following composition was then made up, using this liquid.

Grams Material 79.7 Mobil Chemical Co. 8-8998-001 clear thermoset vinyl 19.5 MEK Toluene 1:1

0.8 Phytic acid boiled with butanol (25% active acid) Viscosity of the coating over a period of 10 days aging was as follows:

Viscosity Time No. 2 Zahn Cup Sec lmmediately after 35 adding modified acid 8 hours 31 72 hours 35 10 days 35 The same composition, except that unmodified phytic acid in the same amount of active phytic acid was tried.

Viscosity change of aging the coating after adding the acid was as follows:

Viscosity Time No. 2 Zahn Cup Sec Immediately after 35 adding phytic acid 8 hours 42 72 hours 57 10 days 57 Similar results were obtained with Mobil 70 682 purple and 70 681A green thermoset vinyls.

The boiled phytic acid-butanol solution after 11 days aging was still fully effective in curing coatings.

EXAMPLE l1 Epoxies were found to cure as well with the modified phytic acid (in butanol) as with the straight acid.

EXAMPLE l2 25percent phytic acid solution (0.8 g.) was added to 100 g. of thermosetting vinyl coatings which were applied on 5,151 and 5,182 (Aluminum Association designation) (can sheet). Degree of cure was determined with MEK rubs as described hereinabove. Results of tests are given in the following table, which includes a comparison with the same compositions applied without the phytic acid.

TABLE Coating weight-4i mgJin.

Conversion contcd Wash coated .0005" 5151 .0005" 5161 .0005" 5151 .0095" 5151 Guru No catalyst Phytic acid N catalyst lhytic acid 10' at 300 F-. 3 5 16-16 19-20 at 350 F 8 10 38 10' at 400 F"... l820 17 20-24 52-55 5 at 400 1" 1215 13-15 Coating weight 6 mgJin.

Conversion coated Wash coated .0135 5151 .0135" 5151 .0135" 5151 .0135" 5151 Cure N0 catalyst Phytic acid No catalyst Phytic acid 10' at 200 F. 0 18-19 100-I- 10 at 250 F--. 1+ 65 2 100+ 10 at 300 F 12 100+ 5 100+ 10 at 350 F- 36-38 100+ 39 100+ 10 at 400 F..- 100+ 100+ 83-85 100+ While the invention has been described in terms of preferred embodiments, the claims appended hereto are intended to encompass all embodiments which fall within the spirit of the invention.

Having thus described my invention and certain embodiments thereof, 1 claim:

1. A method for producing a coating with improved curing characteristics which comprises adding phytic acid to a lacquer containing as essential ingredients a thermosetting vinyl or epoxy resin and a solvent for said resin, applying said lacquer to a substrate, and curing said lacquer on said substrate.

2. The method of claim 1 wherein the lacquer is cured on the substrate at a temperature of less than about 600 F and curing takes place to a thickness of from about 1 mg/in to about 10 mg/in of substrate surface in less than about 10 seconds.

3. The method of claim 1 wherein the substrate is aluminum.

4. The method of claim 1 wherein the substrate is aluminum foil.

5. The method of claim 1 wherein the substrate is aluminum sheet.

6. A method for producing a coating with improved curing characteristics which comprises adding phytic acid to butyl alcohol, boiling said solution of phytic acid and butyl alcohol, adding said solution to a lacquer containing as essential ingredients a thermosetting vinyl or epoxy resin and a solvent for said resin, applying said lacquer to a substrate, and curing said lacquer on said substrate at a temperature of less than about 600 F.

7. The method of claim 6 wherein the substrate is aluminum.

8. The method of claim 6 wherein the substrate is aluminum foil.

9. The method of claim 6 wherein the substrate is aluminum sheet.

10. The method of claim 6 wherein the substrate is aluminum can sheet. 

2. The method of claim 1 wherein the lacquer is cured on the substrate at a temperature of less than about 600* F and curing takes place to a thickness of from about 1 mg/in2 to about 10 mg/in2 of substrate surface in less than about 10 seconds.
 3. The method of claim 1 wherein the substrate is aluminum.
 4. The method of claim 1 wherein the substrate is aluminum foil.
 5. The method of claim 1 wherein the substrate is aluminum sheet.
 6. A method for producing a coating with improved curing characteristics which comprises adding phytic acid to butyl alcohol, boiling said solution of phytic acid and butyl alcohol, adding said solution to a lacquer containing as essential ingredients a thermosetting vinYl or epoxy resin and a solvent for said resin, applying said lacquer to a substrate, and curing said lacquer on said substrate at a temperature of less than about 600* F.
 7. The method of claim 6 wherein the substrate is aluminum.
 8. The method of claim 6 wherein the substrate is aluminum foil.
 9. The method of claim 6 wherein the substrate is aluminum sheet.
 10. The method of claim 6 wherein the substrate is aluminum can sheet. 